Luk et al. 2010

This paper tested brain activation patterns of monolinguals versus bilinguals performing the flanker task, in order to test whether the bilingual and monolingual brains treat interference suppression versus response inhibition differently. They found that bilinguals recruited the same network for interference suppression and response inhibition while monolinguals showed different patterns of activation for the two tasks.

Past research has shown that bilinguals perform differently than monolinguals on a variety of different cognitive tasks, including tasks requiring ignoring certain stimuli. However, on different tasks bilinguals and monolinguals show the same behavioral responses. It is thought that this is due to two different kinds of cognitive control: response inhibition (which requires the inhibition of a simple motor response—something both bi- and monolinguals do all the time) and interference suppression (which is more cognitively demanding as conflict of stimuli cannot be resolved simply). Bilinguals perform more quickly than monolinguals on interference suppression tasks. It has been postulated that this difference arises from the fact that bilinguals are constantly suppressing the language not in use (the interfering language) and thus have a lot more experience in suppressing interference.

In this study bilinguals and monolinguals were presented with the flanker task found below. When presented with an image the participants had to say which direction the red arrow was pointing. During this task, participants were sitting in an fMRI machine and had their brains recorded for each response.

Baseline: No interference as the only arrow present is the red arrow.
Neutral: No additional information is present as the other blocks are not pointing in any direction.
Congruent: All the black arrows are pointing the same way as the red arrow. This facilitates your response (makes it easier). However, when mixed with the incongruent trials, it makes the overall task harder (since the participant has to figure out whether the arrows are pointing the same or opposite way).
Incongruent: All the black arrows are pointing the opposite way from the red arrow. This requires the participant to ignore the black arrow and focus on the red one, which makes the task more difficult. This requires interference suppression. No-go: If X’s surround the red arrow, do not say anything. This is an example of response inhibition.

The following regions showed activation:
For monolingual incongruent trials: left temporal pole and superior parietal cortex.
For bilingual incongruent trials and both mono- and bilingual no-go trials: subcortical areas, fusiform gyri, inferior frontal gyri, supplementary motor area, and inferior parietal region .

Brain activations during the task. Red indicates regions with more activity during incongruent trials in monolinguals and congruent trials in bilinguals. Blue indicates regions with increased activity during incongruent and no-go trials in bilinguals and no-go trials in monolinguals.

What is interesting here is that monolinguals recruit two separate networks for the two tasks (no-go = response inhibition and incongruent trials = interference suppression) whereas bilinguals recruited only one network, i.e. the same network that monolinguals recruited for response inhibition.

The experimenters likewise looked at differences in response time for congruent and incongruent trials versus baseline. They found that better performance for both groups (for both tasks) was associated with increased activity in: bilateral middle occipital gyrus, left fusiform area, left lingual gyrus, bilateral cerebellum, right caudate, and the inferior frontal gyrus. On top of this, bilingual performance on incongruent trials was also associated with increased activation of: bilateral cerebellum, bilaterial superior temporal gyri, left supramarginal gyri, bilateral postcentral gyri, and bilateral precuneus.

A good portion of these areas overlap with the bilingual control network proposed by Abutalebi and Green 2008. This further suggests that these differences in activation patterns between mono and bilinguals arise from the bilingual brain’s unique experience and constant practice of suppressing the interfering language, rather than other factors.

Overall this paper supports the theory that bilinguals and monolinguals use different brain networks for interference suppression but not response inhibition, which parallels previous behavioral findings that bilinguals can perform better on some tasks (interference suppression) but equally as well as monolinguals at other tasks (response inhibition). It is very likely that these differences originate from these different networks of activation employed during these tasks.

Abutalebi J., & Green, D. (2008). Control mechanisms in bilingual language production: Neural evidence from language switching studies. Language and Cognitive Processes, 23, 557-582.

Luk G., Anderson J., Craik F., Grady C., Bialystok E. (2010). Distinct neural correlates for two types of inhibition in bilinguals: Response inhibition versus interference suppression. Brain and Cognition, 74, 347-357.